Sync zoneinfo database with tzdata2020a from ftp://ftp.iana.org/tz/releases
* Morocco's second spring-forward transition in 2020 will be May 31,
not May 24 as predicted earlier. (Thanks to Semlali Naoufal.)
* Canada's Yukon advanced to -07 year-round on 2020-03-08.
* America/Nuuk renamed from America/Godthab.
* Shanghai observed DST in 1919. (Thanks to Phake Nick.)
* To reflect current usage in English better, America/Godthab has
been renamed to America/Nuuk. A backwards-compatibility link
remains for the old name.
For a detailed list of changes, see share/zoneinfo/NEWS.